Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using cardioplegia solution.
Extracorporeal blood handling systems have been developed to oxygenate and circulate the patient's blood while the heart is stopped during surgery. Such systems are often complex, comprising several components, such as a blood pump, oxygenator, venous reservoir, heat exchanger, etc., coupled together by tubing. In a typical previously-known blood handling system configuration, blood is routed from a patient, e.g. from the vena cava or the right atrium, into a venous reservoir, through a blood pump, a heat exchanger, an oxygenator, a filter, and back to the patient via a cannula placed in the aorta. Each of these components, and the tubing segments connecting them, requires a minimum fluid volume to operate and presents a non-native surface area to which the patient's blood is exposed during operation of the system.
The priming volume of a blood handling system is the volume of fluid needed to purge all air from the system prior to use, i.e. to prime the system, and is equal to the total internal volume of the system. The priming fluid, for example, a sterile saline buffered solution with or without donor blood products, is typically intermixed with the patient's blood when the system is in operation. The result is hemodilution, which can decrease the concentration of critical blood components to undesirably low levels, or intermix large amounts of donor blood with the patient's own blood. Donor blood carries with it the risk of exposure to diseases carried by the blood donor.
Typical previously known blood handling systems have average priming volumes of approximately 1.8 liters, with median priming volumes of approximately 1.9 to 2.0 liters. Adding this amount of fluid can dilute the 5 liters of blood in the typical adult patient by almost one-third.
The total non-native surface area of a blood handling system is the sum of all surfaces that come into contact with the patient's blood, including the blood-accessible interior spaces of all components, the surfaces of filters and the oxygenator, and the tubing connecting the patient to the blood handling system and interconnecting the components thereof. It is known that exposure of blood to foreign surfaces is associated with platelet activation and undesirable clotting, thereby typically requiring the administration of large doses of anti-clotting agents, such as heparin. Despite this known drawback, previously known blood handling systems typically include approximately 14 m2 of internal surface area.
In addition to the foregoing volume and surface area considerations, the preparation of previously known blood handling systems by the perfusionist typically requires making eight or more aseptic connections between the tubing and ports on blood handling system components. A tubing set, as used herein, refers to the segments of tubing and couplings typically used when connecting components of a cardiopulmonary bypass system.
The tubing and ports fit tightly together, and are often located in awkward and inaccessible locations, making it both physically tiresome and time consuming to make the required aseptic connections. Moreover, each of these connections represents a potential leak in the system, and air bubbles trapped at the connections can be difficult to dislodge.
Although some blood handling system suppliers have responded to the foregoing problems with pre-assembled tubing sets, these tubing sets are typically custom made in that the lengths of the various tubing segments, particularly the perfusion line, are adapted for each specific blood handling system configuration. This requirement for customization limits the ability to make a useful standardized pre-assembled tubing set.
For the foregoing reasons, it would be desirable to provide a tubing set for use with blood handling systems that provides low internal surface area and low priming volume, thereby reducing platelet activation, hemolysis and hemodilution. Preferably, such a system would reduce or obviate the need to introduce foreign fluids, such as saline or non-autologous blood, into the patient's circulation.
It further would be desirable to provide a tubing set for use with blood handling systems that requires fewer connections between the tubing set and ports on the blood handling system components, to improve both the ease of assembly and the integrity of the system once connected.
It also would be desirable to provide a standardized pre-assembled tubing set that would not need to be customized to the configuration of each blood handling system.